how to write a prety pure c code authenticating the account by yourself. apple's srp proto is standard SRP-6a. some diffrences
c is for cookie
sp selected proto
s salt
i iteration count for pbkdf2_hmac digest iter count
SRP password is not the user input password, apple use pbkdf2_hmac dk as SRP password.
sk ---> sha256 of clear password the size of password is 0x20 bytes.
s2k ---> sha256 of clear password then format bytes to %02x string. so that the size of password is 0x40 bytes.
s4k ---> ask apple for the answer.
the digest info is useful